160 PHOTO-MICROGRAPHS. 
medico-legal cases are the blood of man, and not 
of one of the lower animals named, is likely to 
result in serious error and injustice to the indi- 
vidual whose life may be imperiled by such un- 
warrantable testimony. 
If the question was as between man and a fowl 
or reptile, or one of the Mammalia in which there 
is a considerable difference in size, —as a sheep or 
goat, — there would be no difficulty in determin- 
ing that the blood was zof that of man. 
The red blood-corpuscles of birds, fishes, and 
reptiles have a well-defined central mass or nu- 
cleus, which is not present in those of adult mam- 
mals, but is found in the earlier period of the 
development of the embryo of man and of the 
lower animals of this class. The oval blood-cor- 
puscles of the Camel tribe have no nucleus. 
The general form of the red blood-corpuscles is 
well shown in our photo-micrographs (Plate V.); 
but it must not be supposed that this form is 
rigidly preserved. On the contrary, these little 
colored, biscuit-shaped, or oval masses are ex- 
tremely flexible, and either in the capillaries of a 
living animal or under a thin glass cover may be 
seen to change their shape from contact the one 
with another, or from the slightest pressure. 
The average number of red blood-corpuscles in 
a cubic inch of human blood has been estimated at 
upwards of eighty nullions, The number is consid- 
erably less in certain chronic diseases; and the 
degree of impoverishment may be estimated by 
counting under the microscope the number of 
